The present invention relate generally to braking systems for use in motor vehicles, and more particularly to the use of a magnetostrictive pump assembly for such a braking system.
Generally, conventional braking systems include an accumulator for accumulating hydraulic pressure to be used for the braking operation of the vehicle and further have an apparatus of controlling the hydraulic pressure of the accumulator. The hydraulic pressure in the accumulator is typically controlled by an electric motor-driven pump associated with a pressure sensor which senses the accumulator pressure. The outlet of the pump is connected to the accumulator. The motor-driven pump draws brake fluid from a reservoir and pumps the brake fluid to the accumulator to increase the fluid pressure in the accumulator.
The accumulator pressure control apparatus is operated such that the motor-driven pump is operated in response to the accumulator pressure falling below a predetermined lower limit and deenergized when the accumulator pressure reaches a predetermined upper limit. One problem with such an accumulator pressure control apparatus is that it is difficult to accurately keep the accumulator pressure in a predetermined range due to the delay between actuation and deactivation of the motor and the resulting output from the pump.
Further, such a delay in the pump operation method causes difficulty to quickly stop the pump at the time of termination of the braking operation. This disadvantage is particularly magnified when a slip control or anti-lock brake system is applied to each wheel and integrated with the brake system, as the non-simultaneous actuation of a brake at each wheel increases the delay in stopping the motor and results in generation of noises and vibration due to continued pump operation.